Research

Tufts Micro & Nano Fabrication Facility (TMNF)

Tufts University

Please send examples of research projects being conducted in the lab to Prof. White for inclusion in this page.

Comparison of Techniques for Polysilicon Residual \ Stress Measurements

 

Experimental work comparing wafer curvature measurements, micro-rotating structures, buckling microstructures, and vibrating microstructures for the measurement of residual stresses in thin polysilicon films.

 

Student: Andrew Mueller, ME Masters of Science student. Advisor: Prof. White, ME

SEM images of surface-micromachined polysilicon structures developed at Tufts by Andrew Mueller and Robert White. Fabrication was conducted partly at the Tufts Microfab, partly at the MIT Microsystems Technology Laboratory and partly at the University of Michigan Nanofabrication Facility.

Micromachined Shear Stress Sensors for in-situ Monitoring of Surface Forces in ChemiMechanical Planarization

 

A PDMS microstructure is being developed to measured the interaction forces that occur between a wafer and a polishing pad during CMP.  The PDMS structures deflect in response to fluid forces and solid-solid contact forces.  An optical method is used to monitor structure deflection in-situ.

 

Student: Andrew Mueller, ME Masters of Science student. Advisor: Prof. White, ME

Left: SEM image 30 micron diameter, 100 micron tall PDMS post-in-well developed for the CMP shear stress sensor project.  Right: angled light microscope picture showing a portion of the array with different sized PDMS posts-in-wells.

Micromachined Pressure Sensor Arrays for Aeroacoustic Applications

 

A 8x8 (64 element) acoustic pressure sensor array is being developed to measure high wavenumber components of the pressure field in the turbulent boundary layer during aircraft flight.  The array was designed at Tufts and fabricated by Memscap using the PolyMUMPS process.  The element pitch is 1.2625 mm on center.  Each element of the array is 600 microns in diameter, and is expected to achieve  a bandwidth of 500 Hz—80 kHz with a dynamic range of 85-150 dB SPL.

 

Student: Joshua Krause, ME Masters of Science student.  Advisor: Prof. White, ME

Light microscope image of an array element (left) and SEM image of writing below a wire and pad (right).  The elements are made of 3.5 micron thick polysilicon with a 2 micron air gap to the bottom electrode.  The wires (and writing) are Cr/Au on polysilicon.

Calibration Targets for Dual Emission Laser Induced Fluorescence (DELIF)

 

Calibration wafers have been fabricated to calibrate an optical measurement technique called Dual Emission Laser Induced Fluorescence (DELIF), which is used to determine fluid film thickness between a glass wafer and a polishing pad during Chemical Mechanical Polishing (CMP).  Sqaure wells measuring 1mm² and 0.25mm² are etched into these glass wafers to known depths (up to 130um).  The necessary well etch depth depends on the surface roughness of the polishing pad.  In order for fluid layer thickness difference under the wells to be detectable, the well depth should be at least 3 times the surface roughness of the pad.

 

Student: Caprice Gray, ME PhD student.  Advisors: Prof. Rogers, Prof. Manno, Prof. White, ME

(Left) Photograph of etched glass calibration wafers used to determine thin fluid film thickness during DELIF. (Right) A light microscope picture of a single 1mm² calibration well 23 microns deep.

Micromolding of Aqueous-Derived Silk Structures

 

There is enormous potential for biopolymers in MEMS applications. In MEMS devices biopolymers could function as membranes or optical components. Devices which demand outstanding biocompatibility, such as implantable sensors, could be packed in or fully manufactured from biopolymers materials. The challenge today exists in understanding critical processing parameters in manufacturing structures with micron and submicron level features from biopolymers. In this research, the development of a micromolding technology, to produce microstructures from aqueous derived silk solutions is studied. In particular, well-defined cellular and tissue culture substrate (scaffold) fabrication is used as a model to study manufacturing methods. The manufacturing challenges consist in counteracting shrinkage caused by solvent evaporation, producing well defined porous structures and demolding of delicate structures.

 

Student: Konstantinos Tsioris, ME MS student.  Advisor: Prof Wong, ME

(Left) SEM image of silk fiber (crossection 100 x 100 μm) as part of well defined scaffold layer. (Right) PDMS microchannel system (individual channels: width 100 μm  x height 250 μm) produced with SU-8 photolithography.

Thermal Design and Fabrication of Microscale Heaters

 

Microscale heaters with integrated thermistors were fabricated as an undergraduate research project.  The devices use thin sputtered nickel films for both heating and sensing elements.   The processes involved were standard photolithography, sputtering, and liftoff. Some of the heaters were functional, and some failed. Residual stresses, particles, and/or human error in processing appear to have caused the observed defect in some of  the heater lines.

 

Student: Michael Rizzolo, ME undergraduate.  Advisor: Prof Wong, ME

Lab-on-a-chip Devices for Dynamic Seeding of Bone Cells

 

Lab-on-a-chip devices have become increasingly popular as quick and easy diagnostic and experimental tools due to their size, flexibility in application, and relative ease of manufacturing and use. The development of customizable lab-on-a-chip features, such as surface patterning or coatings, can have widespread application. This research established low-cost and simple calcium phosphate coating capabilities on a silicon wafer using electrophoretic deposition, as well as the ability to pattern such a coated wafer with photoresist. The coated and patterned wafer was used to evaluate the ability of bone cells to adhere to a microchannel surface under flow, or dynamic seeding conditions.

 

Student: Erica Belmont, ME MS student.  Advisor: Prof Matson, ME

(Top Left) Silicon wafers, diced to 36mmx36mm, coated with calcium phosphate and one uncoated wafer chip for comparison (Bottom Left) Calcium phosphate coated wafers with microchannels patterned in 100um thick SU-8 photoresist (Right) SEM image showing cross-section of calcium phosphate coating, approximately 15um thick, on silicon wafer

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